feat: message previews

- Remove partial downloads (remove creation of the stub messages) (#7373)
- Remove "Download maximum available until" and remove stock string `DC_STR_DOWNLOAD_AVAILABILITY` (#7369)
- Send pre-message on messages with large attachments (#7410)
- Pre messages can now get read receipts (#7433)

Co-authored-by: Hocuri <hocuri@gmx.de>

deltachat-jsonrpc/src/api/types/message.rs

@@ -92,6 +92,9 @@ pub struct MessageObject {
 
     file: Option<String>,
     file_mime: Option<String>,
+
+    /// The size of the file in bytes, if applicable.
+    /// If message is a pre-message, then this is the size of the to be downloaded file.
     file_bytes: u64,
     file_name: Option<String>,